This invention relates generally to the fabrication of fuel pin elements employed in nuclear reactors and, more particularly, to a magnetic pushrod assembly for moving stacked fuel pellets and the like between workstations.
The reactor core of a typical nuclear reactor generally contains a multiplicity of similarly constructed and interchangeable fuel assemblies vertically oriented in a side-by-side relation. Each fuel assembly, in turn, contains a multiplicity of thin, elongated fuel elements or pins, each comprised of a thin-walled tube or cladding containing a suitable fissionable material, such as plutonium, uranium and/or thorium for example, in the form of cylindrical fuel pellets stacked end-to-end therein. Also, a number of so called "cold components", such as tag gas capsules, reflectors, springs, spacers and the like, are enclosed within the cladding behind the fuel pellets.
Various methods are known for handling these loose stacks of fuel pellets and cold components and ultimately loading them into the cladding of a fuel pin. Special safeguards must be practiced when moving and loading fuel pellets formed of plutonium and/or reprocessed uranium compounds because of their toxic nature to preclude the release of radioactive contaminants to the atmosphere and to prevent overexposure to personnel.
In recent years, automated fuel pellet handling and loading systems have been developed to handle and transport the fuel pellets, cold components and cladding within fully enclosed fabrication and assembly stations without contaminating the area and personnel outside these enclosed assembly stations. Often, a number of fuel pellets and/or cold components in a juxtaposed end-to-end relation must be axially moved from one station to another during the assembly process prior to and during loading into the cladding. One serious problem in shifting these loosely assembled stacks axially is the application of excessive forces, such as might occur during pellet or cold component jamming or binding. Such forces not only damage the fuel pellets and cold components, but also can impair the associated equipment, resulting in expensive and time consuming repair as well as production down time.
Various two-part, disengageable electro-mechanical force sensing devices or mechanical snap-action arrangements are known for limiting the forces applied in a pushrod application. However, these known devices include moving parts susceptible to wear over a period of time with a resultant change in their force limiting settings, thereby aborting their intended purposes. Moreover, these two-component assemblies are difficult to re-engage after separation since they require a force to do so.